In recent years, optical communication network enabling large capacity data communication at high speed is expanding. The optical communication network is assumed to be mounted on a consumer device in the future. An electrical input/output optical data transmission cable (optical cable) capable of being used no different from the present electrical cable is desired for the application of large capacity data transfer at higher speed, noise countermeasures, and data transmission between substrates in the device. In view of flexibility, a light guide is desirably used for the optical cable. A light transmission path will be described below as the light guide, but includes light transmission paths such as an optical fiber.
The light guide is formed by a core having a large index of refraction and a clad having a small index of refraction arranged in contact with the periphery of the core, and propagates the light signal entered to the core while repeating total-reflection at the boundary of the core and the clad. The flexibility can be enhanced by using a flexible polymer material for the core and the clad of the light guide.
In recent years, in particular, a flexible (similar to electrical wiring) optical wiring mounted on bendable displays and smaller and thinner consumer devices is desirably realized with the light guide. That is, the light guide is desirably a film-form light guide.
The photoelectric conversion elements (optical elements) need to be aligned and optically coupled to transmit the optical data using the light guide. The optical element converts an electrical signal to a light signal and emits the same, or receives a light signal and converts the same to an electrical signal. In order to maintain such an optically coupled state, the distance and the positional relationship of a light receiving/transmitting unit of the light signal in the optical element fixed with the optical cable and the incident/exit port of the light signal in the light guide need to be maintained constant.
In a package mounted with the flexible light guide and the optical element, a manufacturing method of a package capable of realizing the positional accuracy of the flexible light guide end and the optical element is desired. Generally, the package includes an accommodating portion for accommodating the optical element and a supporting portion for supporting the flexible light guide. A lead frame connecting with the optical element is arranged in the package.
Patent Document 1 discloses a manufacturing method of a semiconductor device, where in such a manufacturing method, a lead frame mounted with an IC chip is set in the die, and resin sealing is performed with the four corners of a die pad held down with upper and lower movable pins.
Patent Document 2 discloses a manufacturing method of a semiconductor device, where a lower surface electrode of a silicon surge absorber chip is fixed on a copper substrate using a solder, the head of the lead frame is soldered to an upper electrode of the chip, and the chip is covered by molding resin so as to expose part of the substrate.
However, the techniques disclosed in Patent Documents 1 and 2 have the following problems when applied to the manufacturing method of the package mounted with the light transmission path and the optical element.
First, in Patent Document 1, resin sealing is performed with the four corners of the die pad held down with the upper and lower movable pins. A warp etc. produces at the lead frame (die pad mounting surface) immediately below the die pad if the four corners of the die pad are simply held down. In a normal semiconductor device, the warp etc. of the die pad mounting surface does not influence the operation of the semiconductor device. In the package mounted with the flexible light transmission path and the optical element, however, high accuracy is demanded on the positional relationship of the flexible light transmission path end and the optical element. In particular, a package in which the positional accuracy of the light guide mounting surface and the optical element mounting surface is high is necessary. Thus, the warp tends to easily produce at the optical element mounting surface, and manufacturing at the demanded positional accuracy becomes difficult even if the technique disclosed in Patent Document 1 is applied and the package is manufactured with the four portions of the optical element mounting surface in the lead frame held down with the upper and lower movable pins.
In the semiconductor device of Patent Document 2, since the chip mounting portion is held with one side of the substrate, the positional accuracy with the mold resin is difficult.    Patent Document 1: Japanese Laid-Open Patent Publication “Japanese Laid-Open Patent Publication No. 11-111746 (date of publication: Apr. 23, 1999).    Patent Document 2: Japanese Laid-Open Patent Publication “Japanese Laid-Open Patent Publication No. 6-151699 (date of publication: May 31, 1994).